1. Field of the Invention
The present invention relates to printers, and more particularly, to printers having a multiple print element printhead.
2. Background of the Invention
Many printers have a printhead which is placed in physical proximity to the printing medium (such as paper) on which an image is to be imprinted. The printhead typically has one or more print elements such as print wires or ink jets, each of which can imprint a dot or other picture element (pixel) on the print medium. The printhead is usually scanned back and forth across the print medium in a raster motion until the entire image has been printed.
To reduce the required number of scans, printheads may have as many as 33 print elements vertically aligned on the printhead. Selected ones of the print elements are actuated in accordance with data provided to the printhead by the printer as the printhead is scanned across the printing medium. The format of the data provided to the printhead is necessarily a function of the number and arrangement of the print elements of the printhead. However, different models of printers from different manufacturers and even from the same manufacturer often have different types of printheads. As a consequence, customized circuitry has often be required for each different printhead to provide the pixel data format required by the particular printhead type. SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved printer obviating, for practical purposes, the above mentioned limitations, particularly, in a manner requiring a relatively uncomplicated electronic arrangement.
These and other objects and advantages are achieved in a printer which in accordance with the illustrated embodiment, generates a bit mapped raster matrix of an image to be printed, and accesses from the matrix, a group of bits corresponding in number to the number of printing elements of the printhead. This group of bits is used to drive the printing elements of the printhead so as to print the image. In printers having raster scanning printheads, the selected groups of bits are accessed from the bit mapped raster matrix synchronously with the raster scanning of the printhead.
For example, the printhead of the printer of the illustrated embodiment is a raster scanning printhead having 33 printing elements displaced vertically in a single vertical column. Thus, the printhead is capable of printing 33 adjacent scan lines during each pass of the raster scan of the printhead. To prepare print data in a format acceptable to the print engine of the printer, the printer converts the image to be printed into a two-dimensional raster matrix of pixels. In the illustrated embodiment, each print element of the printhead is a print wire or pin which, when actuated, imprints a dot on the printing medium which is typically paper. Each pixel of the raster matrix of pixels corresponds to a dot to be imprinted or not imprinted on the printing medium depending upon the value of the pixel data.
Scanning from left to right and starting at the top of the image to be printed, the printer accesses the first group of 33 pixels in each column of pixels in the matrix, one column at a time, and applies the bit data for those 33 pixels to the print engine in time for the print wires of the printhead to be actuated in accordance with the 33 bits of the pixel data. As the printhead continues to scan, the printer accesses the first group of 33 pixels of the next column of the raster matrix of pixels and supplies that pixel data to the print engine. This process is continued until the printhead reaches the end of the scan line. At this point 33 rows of pixel data, referred to herein as a "segment," have been processed.
In the illustrated embodiment, the printhead alternates between left to right and right to left motions as each scan line is completed. Thus, after the first scan line has been scanned, the printing medium is advanced to move the next scan line into position for the printhead which then initiates scanning in a right to left motion. Consequently, the printer accesses the second group of 33 pixels in the last column of the raster matrix of the pixels as the printhead initiates the right to left scan. The second group of 33 pixels is sequentially accessed from each succeeding column until the first column of the raster matrix is again reached. This process is repeated for each subsequent segment of the raster matrix until the entire image has been printed.
It should be appreciated that the above architecture is readily adaptable to many different types of printheads having a variety of print element arrangements. Thus, if the printhead has 22 print elements rather than 33 print elements, the procedure is readily modified so as to sequentially access groups of 22 pixels rather than 33 as each scan line segment is processed. Additional advantages will be apparent from the following more detailed description.